Dimers of magnetic transition ions with a strong spin exchange coupling have a series of spin states with S=0, 1, 2SM where SM is the spin state of one ion. The zero-field parameters in the Spin-Hamiltonian of each spin state are due to three interactions: (1) spin-spin interactions within one ion, (2) dipole-dipole interaction between the ions, and (3) anisotropy in the spin-exchange interaction. Measurement of the Spin-Hamiltonian for more than one spin state allows us to separate out these individual contributions and is the only way to determine the amount of anisotropy in the spin-exchange interaction. These measurements require application of W-band (95 GHz) spectroscopy at low (cryogenic) temperatures.